A large number of switching converters have become known for the supply of electronic devices, wherein a distinction is made between flyback converters and forward converters; however, mixed types have also become known. Complicated solutions meet the greatest variety of requirements regarding performance, short circuit-proofness, noiselessness, etc.
There are cases, in which for the current supply of smaller devices, e.g., even the control circuit of a switching converter, an auxiliary current supply is needed, on which special electrical requirements are not placed, which, however, will not noticeably affect the costs of the actual device, e.g., of a switching converter. Autonomous flyback converters, in which the presence of a transformer with an additional auxiliary winding is, however, required, are often used in such cases. One of many examples of such a flyback converter can be taken from, for example, DE 30 07 566 A1.
U.S. Pat. No. 5,227,964 relates to a switching power supply with a transformer. An AC voltage is converted by means of a rectifier to a DC voltage, the latter being switched by a switching transistor to a primary winding of the transformer and the corresponding AC voltage at the secondary winding being converted by means of a two way rectifier into an output DC-voltage. The voltage across a measurement resistor on the primary side is compared with a reference voltage and an amplifier supplies an overcurrent shut-off signal to the control circuit of the switching transistor in order to limit the output current.